This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The studies undertaken in this work focus on the cellular and molecular mechanisms used by cells in the vertebrate retina to process visual information. In particular, we have been examining the hypothesis that hydrogen ion release regulated by horizontal cells might play an important role in modulating neuronal signals in the outer retina. Horizontal cells are second order neurons that receive direct connections from photoreceptors and are thought to send inhibitory feedback signals onto photoreceptor synaptic terminals and feed forward inhibitory signals onto the dendrites of bipolar cells. The molecular mechanisms used by horizontal cells to provide this inhibition remain under debate. One hypothesis that has received recent experimental support suggests that horizontal cells release H+ which then bind to calcium channels on photoreceptor synaptic terminals, leading to the closure of voltage-gated calcium channels and a consequent reduction in the release of neurotransmitter.